Currently, a variety of additives are used to control specific performance characteristics of lubricating oil. For example, detergents such as highly basic metal salts are useful for keeping the insoluble particulate materials in an engine or other machinery in suspension. Dispersants, such as succinimides having molecular weight from about 700 to about 10,000, also maintain oil insolubles in suspension in the fluid, thus preventing sludge flocculation and precipitation or deposition of particulates on metal parts. Anti-oxidants such as dioctylphenylamine and phenyl-alpha-naphthylamine reduce the tendency of mineral oils to deteriorate in service. This deterioration can be evidenced by the products of oxidation such as sludge and varnish-like deposits on the metal surfaces, and the formation of soot and the concomitant increase in viscosity caused by soot in the oil.
Graft polyolefins containing nitrogen-containing and/or oxygen-containing monomers for use as dispersant viscosity index improvers are also known. U.S. Pat. No. 5,523,008, the disclosure of which is incorporated herein by reference in its entirety, describes a grafted polyolefin containing at least about 13 moles of N-vinylimidazole or other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing monomers per mole of a grafted polyolefin backbone. Also described is a lubricating oil comprising a lubricant base oil and a grafted polyolefin as described above as well as a method of making a dispersant-viscosity index improver. N-vinylimidazole or other ethylenically unsaturated nitrogen-containing and/or oxygen-containing monomers and a graftable polyolefin are reacted with sufficient initiator to graft at least about 13 moles of the monomer to each mole of the polyolefin.
U.S. Pat. No. 5,663,126, and U.S. Pat. No. 6,686,321, the disclosures of which are incorporated herein by reference in their entireties, describe a grafted polyolefin containing one or more of N-vinylimidazole, 4-vinylpyridine, or other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing graftable monomers grafted to a polyolefin copolymer. Also described are lubricating oil compositions comprising a lubricant base oil and a grafted polymer as described above as well as methods of making dispersant viscosity index improvers.
Each of the additives is a separate component of the formulated lubricating oil and adds cost. Thus, it would be beneficial to have a multi-functional additive that controls more than one performance characteristic of the lubricating oil.
We have now discovered a novel multi-function graft polymer useful as an additive for lubricating oil compositions to control soot, sludge, and varnish as well as viscosity increase.